Invasive disease caused by Haemophilus influenzae: the sensitivity of statutory reporting

The objective of the study was to investigate the sensitivity of the statutory reporting of Haemophilus influenzae invasive disease (HIID) during the period between 1996 and 1997 in Catalonia, Spain.

The incidence of HIID reported passively by clinicians was compared with the cases detected by a system of microbiological surveillance. In all cases isolated, the age of the patient, the clinical form and the serotype were investigated.

Sixty-six cases were passively reported and 111 were detected by microbiological surveillance. Overall sensitivity of reporting was 59.5% (95% CI, 50.7-69.1), with differences being observed according to the variables studied. The highest values were obtained in children under 5 years (87.8%; 95% CI, 73.7-95.9), in cases with meningitis and/or sepsis (64.3%; 95% CI, 50.4-76.6) and in serotype b (73.0%; 95% CI, 60.3-83.4). In the logistical regression analysis, only age under 5 years was associated with greater reporting (OR= 9.8; 95% CI, 2.5-37.8).

Reported morbidity in children under 5 years is a good estimate of the true incidence of HIID in Catalonia (underreporting was 12.2%), but not for those above this age in whom the underreporting was 57.2%.